The present invention relates to liquid crystal display devices with TFTs (Thin Film Transistors) and methods of manufacturing the same.
Conventionally, TFT liquid crystal display devices are widely used to display high quality images. The following description will discuss a method of manufacturing a semiconductor substrate in such liquid crystal display devices.
The basic structure of the TFT included in such liquid crystal display devices is of a reverse stagger type; therefore, the gate electrode provided in the bottom layer is preferably made of a metal that can be selective etched. Here, the description will be based on an assumption that a Ta metal film is used as a material for the gate electrode as illustrated in FIG. 6(a) and FIG. 8(b).
First, as shown in FIG. 6(a), a gate electrode 52 composed of a Ta metal film is deposited on a glass substrate 51 using a PVD technique (Physical Vapor Deposition technique, which is a sputtering technique).
Next, as shown in FIG. 6(b), a resist 53 is deposited on the gate electrode 52 and patterned as required for the gate electrode 52 using a photolithography technique.
Then, as shown in FIG. 6(c), the gate electrode 52 is fabricated into a predetermined electrode pattern using a PE (Plasma Etching) technique, a RIE (Reactive Ion Etching) technique, or a wet etching technique, and the resist 53 is removed.
Then, as shown in FIG. 6(d), a GI (Gate Insulator) film 54 (typically composed of SiNx), an Ixe2x80x94Si film 55, and a n+ film 56 are successively formed, typically, using a PE-CVD technique (Plasma-Enhanced Chemical Vapor Deposition technique).
After forming these three films, similarly to the patterning of the gate electrode 52, the Ixe2x80x94Si film 55 and the n+ film 56 that constitute a channel layer are fabricated like an island as shown in FIG. 7(a) using a photolithography technique as well as a PE (plasma etching) technique, an RIE (Reactive Ion Etching) technique, or a wet etching technique so as to form a semiconductor layer.
Thereafter, a resist (not shown) is applied on the gate insulator film 54 according to a pattern, and the gate insulator film 54 is etched above the connecting terminal section of the gate electrode 52. Typically, the gate electrode 52 serves as the connecting terminal.
Subsequently, as shown in FIG. 7(b), a source electrode 57 (source and drain electrodes in the strict sense of the terms; however since the drain electrode is formed simultaneously with the source electrode, they may be collectively referred to as the source electrode) of Ti, Al, W, Ta, etc. is deposited using a PVD technique, and patterned using the same method as that used to form the gate electrode 52.
Subsequently, using the same source mask as that used in the patterning of the source electrode 57, the n+ film 56 is etched off the channel section to form a TFT (Thin Film Transistor) 58 (see FIG. 7(c)).
Thereafter, a pixel electrode 59 composed of a transmissive conductive film (typically, an ITO film) is deposited using a PVD technique as shown in FIG. 7(d), and fabricated into a predetermined electrode pattern using a wet etching technique as shown in FIG. 8(a).
Lastly, as shown in FIG. 8(b), a TFT protection film 60 is formed using a PE-CVD technique, completing the manufacturing process of a TFT array substrate.
Incidentally, in recent years, a low resistance metal, such as Al, an Al alloy, or Cu, is used to constitute electrodes in a high precision liquid crystal display panel (see Japanese Laid-Open Patent Application No. 6-148683/1994 (Tokukaihei 6-148683: laid-open on May 27, 1994), Japanese Laid-Open Patent Application No. 7-169967/1995 (Tokukaihei 7-169967: laid-open on Jul. 4, 1995), and Japanese Laid-Open Patent Application No. 10-253976/1998 (Tokukaihei 10-253976: laid-open on Sep. 25, 1998) for examples). However, if, for example, the gate electrode 52 is composed of the foregoing Al material instead of Ta, and the source electrode 57 is composed of an Al material, a defect in the gate insulator film 54 causes the gate electrode 52, which lies beneath the source electrode 57, to erode during the etching of the source electrode 57.
A further problem arises during the wet etching of the ITO film, which is the last step, that the gate electrode 52, as well as the source electrode 57, erodes because of the use of HCl, HBr, or other strong acids, unless a sufficiently thick insulator film (for example, the gate insulator film 54) is provided.
Nonetheless, it is difficult to form a thick inorganic insulator film, because its formation and etching steps are time-consuming and an undesirable electrostatic capacity is created between those electrodes provided above and below the thickened insulator film.
Japanese Laid-Open Patent Application No. 4-163528/1992 (Tokukaihei 4-163528: laid-open on Jun. 9, 1992) discloses a technology to protect the pixel electrode from peeling during patterning by depositing the pixel electrode over two interlayer insulator films. The interlayer insulator films in such a configuration have a double-layered structure constituted by an organic insulator film and an inorganic insulator film that is formed on the organic insulator film.
Therefore, in the etching process of the interlayer insulator films, the inorganic film is subjected to dry etching (the total thickness of the film is 3.13 xcexcm), which is followed by etching of the organic film. Here, the organic film is thick and inevitably needs to be etched using a liquid agent. A problem arises, however, that acid and alkaline solutions and other liquid agents that erode the Al material constituting the Al electrode can not be used in the treatment of the organic film. Another problem is that the organic film is more likely to cause source-to-drain leakage than the inorganic film.
The aforementioned problems of the source electrode 57 and the gate electrode 52 composed of Al materials are summed up as below:
(1) A defect in the gate insulator film 54 causes the gate electrode 52 and the terminal section formed from the gate electrode 52 to be etched during the patterning of the source electrode 57.
(2) During the patterning of the pixel electrode 59 composed of an ITO film, the source electrode 57 and the gate electrode 52 erode, as the strong acid liquid, such as HCl used for the etching of the pixel electrode 59 seeps through defects in the gate insulator film 54. A possible solution that would offer protection to the Al electrode from erosion is to modify the foregoing manufacturing process so as to form an ITO film on the TFT protection film; however, a simple change in the process could not give satisfactory results in protecting the Al electrode from erosion.
(3) If the pixel electrode is deposited over an interlayer insulator film having a double-layered structure constituted by an organic insulator film and an inorganic insulator film that are sequentially deposited, available chemical agents are limited by the need to protect the Al material for the Al electrode from erosion during the etching of the thickened organic film.
Further, erosion of the foregoing Al electrodes, i.e., the source electrode 57 and the gate electrode 52 reduces the output of good quality liquid crystal display devices, and accordingly adds to the manufacturing cost.
The present invention has objects to offer a liquid crystal display device that is capable of preventing erosion of an Al material of which the source or gate electrode of the liquid crystal display device is composed, and to offer a method of manufacturing such a liquid crystal display device.
In order to achieve the objects, a liquid crystal display device in accordance with the present invention includes:
a first electrode having an Al or Al alloy layer;
a pixel electrode provided above the first electrode, and
at least two interlayer insulator layers interposed between the first electrode and the pixel electrode so as to cover the first electrode, and is characterized in that
the two interlayer insulator layers include a first layer composed of an inorganic insulator film and a second layer composed of an organic insulator film, the first and second layers being provided in this sequence when viewed from the first electrode.
A method of manufacturing a liquid crystal display device in accordance with the present invention is characterized in that it includes the steps of:
providing a first electrode having an Al or Al alloy layer;
depositing at least a first layer composed of an inorganic insulator film and a second layer composed of an organic insulator film above the first electrode so as to provide at least two interlayer insulator layers that cover the first electrode, the first and second layers being provided in this sequence when viewed from the first electrode; and
providing a pixel electrode above the interlayer insulator layers.
According to the arrangement, the pixel electrode is disposed at least above the two interlayer insulator layers formed by depositing the first layer composed of an inorganic insulator film and the second layer composed of an organic insulator film, the first and second layers being provided in this sequence when viewed from the first electrode. Therefore, for example, when the organic insulator film is etched using a weak alkaline solution, the inorganic insulator film provides protection to the underlying first electrode having an Al or Al alloy layer by preventing the etching liquid from reaching the first electrode. The first electrode is thus protected from erosion.
Moreover, one less photo masks are required in the patterning of the two interlayer insulator layers, by using the same pattern in the patterning of the organic insulator film (3 xcexcm thick) in the photolithography step and in the following patterning of the inorganic insulator film (TFT protection film, 0.13 xcexcm thick) by dry etching. The arrangement offers good selectivity that allows selective etching of the inorganic insulator film, while providing protection to the underlying first electrode having an Al or Al alloy layer.
Further, the arrangement allows the pixel electrode to be substantially separated by the interlayer insulator layers from the first electrode, for example, the source electrode or the gate electrode. Therefore, the arrangement successfully protects the Al or Al alloy layer in the first electrode from erosion during the etching of the pixel electrode despite a possible defect in either of the interlayer insulator layers. Leakage can be also prevented between the pixel electrode and the first electrode.
In the foregoing arrangement, the first layer composed of an inorganic insulator film is preferably provided directly on the first electrode (metal electrode) composed of an Al or Al alloy layer.
According to the arrangement, the first layer composed of an inorganic insulator film is formed directly on the first electrode (metal electrode) composed of an Al or Al alloy layer; therefore, the inorganic insulator film is formed with high quality, in comparison to a conventional arrangement including an inorganic insulator film formed on an organic insulator film. Further, the organic insulator film in the second layer can be formed on the inorganic insulator film in a satisfactory manner.
In other words, by forming the interlayer insulator films on the first electrode in the sequence as set forth in the present invention (an organic insulator film over an inorganic insulator film), the interlayer insulator films are formed with satisfactory quality. This results in less defects occurring in the interlayer insulator films, successfully preventing the etching liquid from reaching the metal electrode through the defects and thus protecting the metal electrode from erosion during the patterning of the pixel electrode.
Further, in the foregoing arrangement, preferably, the first layer composed of an inorganic insulator film is a TFT protection film.
According to the foregoing arrangement, the TFT protection film provided on the first electrode plays another role as an inorganic insulator film; this restrains increase in the number of interlayer insulator films, which otherwise would add to the complexity of the structure of the liquid crystal display device.
For a fuller understanding of the nature and advantages of the invention, reference should be made to the ensuing detailed description taken in conjunction with the accompanying drawings.